1. Field of the Invention
The present invention relates to a fastening element, such as, bolt, nail, and the like, to be driven in a constructional component formed of a hard material, e.g., concrete, by a high-pressure gas-operated setting tool and including a load application section, a stem adjoining the load application section, a tip adjoining the stem, a prestress member having a force-introducing section engaging at least one of the stem and the tip, and a bearing surface remote from the load application section.
2. Description of the Prior Art
Fastening elements, such as nail, bolts, and the like and which are made of steel, are used for securing objects to constructional components formed, e.g., of concrete or stone. A fastening element has a stem with a usually narrowing tip, and a load application section provided at the end of the fastening element remote from the tip. The load application section can be formed, e.g., as a threaded section or a head. The setting process is effected, e.g., with an explosive charge-operated or gas-operated setting tool. During a setting process, the fastening element, when reaching, e.g., concrete, often causes chipping-off of the concrete or formation of cracks therein. This damage results in that the setting process needs to be repeated with increased operational costs and/or chipped-off areas and cracks should be treated and, in case of an exposed concrete, covered.
German Publication De-44 32 783 A1 discloses a fastening element, a nail or bolt with a prestress element being surrounded with another element formed of a plastic material for increasing the bearing surface over which the fastening element is supported on a constructional component. The introduction of forces is effected over a sleeve section of the prestress element in which, in the initial position of the fastening element, the tip of a nail, a bolt or the like is located.
German Publication DE-19 10 723 discloses a fastening element, nail, bolt, in which a metal washer is arranged on the stem rearwardly, with respect to the setting direction, of a disc of an elastic material. The disc has a diameter smaller than the stem diameter, so that the press-on effect is somewhat small during the setting process.
The drawback of the known fastening elements consists in that, on one hand, with uneven surfaces of the constructional component, cracks often are formed during the setting process and, on the other hand, the fastening element does not tightly abut the constructional component because of arching of the component during the setting process. As a result, a gap is formed between the bearing surface and the constructional component.
Accordingly, an object of the present invention is a fastening element in which the drawbacks of the conventional fastening elements are eliminated and the failure rate of the setting process is substantially reduced.
This and other objects of the present invention, which will become apparent hereinafter, are achieved by providing on the bearing surface of the prestress member an elastic or compressible layer which during and after the setting process, is located between the bearing surface and the constructional component. In the middle of the layer, there is provided an opening the diameter of which is greater than the diameter of the stem of the fastening element and, preferably, greater than the diameter of flange-shaped bearing section of the prestress member. During the setting process, the elastic layer provides for an optimal transmission of the setting energy to the surface surrounding the setting point even with a rough and uneven surface of the constructional component. As a result no chipping-off occurs. The radial spacing of the elastic layer from the setting axis or from the stem of the fastening element and the central opening therein provide for a free space into which during the setting process; the material, which is produced during the setting process, can flow. With the present invention, lifting of the fastening element and/or gap formation between the bearing surface and the constructional component is prevented. Prevention of lifting of the fastening element off and prevention of the gap formation were established during comparative tests of the inventive fastening element and a conventional one.
It is advantageous when the bearing surface is formed of two elements the end surfaces of which facing in the setting direction, lie in the same plane. The two elements can be formed by a flange-shaped bearing section of the prestress member and a bending-resistant disc surrounding the bearing section. The bending-resistant disc can be formed, e.g., of metal and can be provided in order to increase its stiffness, with a circumferential edge arch and/or with beads provided on the surface of the disc facing in a direction opposite to the setting direction. The disc can have the side thereof facing in the direction opposite the setting direction, formed as a bell or a plate.
The formation of the bearing surface by two separate parts permits to reduce manufacturing costs of the prestress member. However, the prestress member and the disc can be formed as a one-piece part.
Advantageously, a metal washer is arranged on the stem of the fastening element rearwardly, with respect to a setting direction of the fastening element; of the force-introducing section of the prestress member. During the setting process, the metal washer is displaced against the force-introducing section, which is formed as a sleeve, folding the same.
The metal washer can be provided with an arch-shaped circumferential edge section During the setting process, the arch-shaped section of the metal washer splices and rolls up the sleeve-shaped force-introducing section so that the later is almost completely folded on is rolled up, which permits to obtain a maximum possible setting depth of the fastening element. This positively affects the force/time behavior of the fastening element.
Advantageously, the metal washer is provided, on its side facing in the setting direction, with one or more cutting elements which splice the sleeve-shaped, force-introducing section in several parts during the setting process. The splicing of the force-introducing section leads to a more rapid folding or rolling-up of this section, which further increases the setting depth of the fastening element.
The novel features of the present invention, which are considered as characteristic for the invention, are set forth in the appended claims. The invention itself, however both as to its, construction and its mode of operation, together with additional advantages and objects thereof, will be best understood from the following detailed description of preferred embodiments, when read with reference to the accompanying drawings.